sysfs: add NetClassPCIDevice and PciDeviceVFAddress for SR-IOV support

Add two new functions to support SR-IOV network VF metrics collection:

- NetClassPCIDevice(iface string) (*PciDevice, error) in net_class.go:
  Resolves /sys/class/net/<iface>/device symlink and returns the backing
  PciDevice using the existing PCI device parser. This gives callers
  access to all PCI device properties (NumaNode, link speed, SR-IOV
  fields, etc.).

- PciDeviceVFAddress(device *PciDevice, vfIndex uint32) (string, error)
  in pci_device.go: Returns the PCI BDF address of a Virtual Function by
  resolving the virtfn symlink at /sys/bus/pci/devices/<bdf>/virtfn<n>.

Test fixtures added under testdata/fixtures/sys/class/net/enp3s0f0/
using the existing 0000:a2:00.0 PCI device fixture.

Signed-off-by: Anthony Harivel <aharivel@redhat.com>

Author: aharivel

sysfs/net_class.go

@@ -97,6 +97,18 @@ func (fs FS) NetClassByIface(devicePath string) (*NetClassIface, error) {
 }
 
 // NetClass returns info for all net interfaces (iface) read from /sys/class/net/<iface>.
+// NetClassPCIDevice returns the PciDevice backing the given network interface
+// by resolving the /sys/class/net/<iface>/device symlink and parsing the
+// corresponding PCI device via the existing PCI device parser.
+func (fs FS) NetClassPCIDevice(iface string) (*PciDevice, error) {
+	deviceSymlink := fs.sys.Path(netclassPath, iface, "device")
+	resolved, err := os.Readlink(deviceSymlink)
+	if err != nil {
+		return nil, fmt.Errorf("failed to resolve device symlink for %q: %w", iface, err)
+	}
+	return fs.parsePciDevice(filepath.Base(resolved))
+}
+
 func (fs FS) NetClass() (NetClass, error) {
 	devices, err := fs.NetClassDevices()
 	if err != nil {

sysfs/net_class_aer_test.go

@@ -50,6 +50,7 @@ func TestAerCounters(t *testing.T) {
 
 	ac, _ := fs.AerCounters()
 	aerCounters := AllAerCounters{
+		"enp3s0f0": AerCounters{Name: "enp3s0f0"},
 		"eth0": AerCounters{
 			Name: "eth0",
 			Correctable: CorrectableAerCounters{

sysfs/net_class_sriov_test.go

@@ -0,0 +1,93 @@
+// Copyright The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build linux
+
+package sysfs
+
+import (
+	"testing"
+)
+
+func TestNetClassPCIDevice(t *testing.T) {
+	fs, err := NewFS(sysTestFixtures)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	dev, err := fs.NetClassPCIDevice("enp3s0f0")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if want := 0xa2; dev.Location.Bus != want {
+		t.Errorf("NetClassPCIDevice() Bus = %#x, want %#x", dev.Location.Bus, want)
+	}
+
+	if dev.NumaNode == nil {
+		t.Fatal("expected NumaNode to be set")
+	}
+	if want := int32(1); *dev.NumaNode != want {
+		t.Errorf("NumaNode = %d, want %d", *dev.NumaNode, want)
+	}
+}
+
+func TestNetClassPCIDeviceMissing(t *testing.T) {
+	fs, err := NewFS(sysTestFixtures)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	_, err = fs.NetClassPCIDevice("nonexistent")
+	if err == nil {
+		t.Error("expected error for non-existent interface, got nil")
+	}
+}
+
+func TestPciDeviceVFAddress(t *testing.T) {
+	fs, err := NewFS(sysTestFixtures)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	dev, err := fs.NetClassPCIDevice("enp3s0f0")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	got, err := fs.PciDeviceVFAddress(dev, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if want := "0000:a2:01.0"; got != want {
+		t.Errorf("PciDeviceVFAddress() = %q, want %q", got, want)
+	}
+}
+
+func TestPciDeviceVFAddressMissing(t *testing.T) {
+	fs, err := NewFS(sysTestFixtures)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	dev, err := fs.NetClassPCIDevice("enp3s0f0")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	_, err = fs.PciDeviceVFAddress(dev, 99)
+	if err == nil {
+		t.Error("expected error for non-existent VF, got nil")
+	}
+}

sysfs/net_class_test.go

@@ -32,11 +32,15 @@ func TestNewNetClassDevices(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	if len(devices) != 1 {
-		t.Errorf("Unexpected number of devices, want %d, have %d", 1, len(devices))
+	found := false
+	for _, d := range devices {
+		if d == "eth0" {
+			found = true
+			break
+		}
 	}
-	if devices[0] != "eth0" {
-		t.Errorf("Found unexpected device, want %s, have %s", "eth0", devices[0])
+	if !found {
+		t.Errorf("expected device eth0 not found in %v", devices)
 	}
 }
 
@@ -94,6 +98,7 @@ func TestNetClass(t *testing.T) {
 	)
 
 	netClass := NetClass{
+		"enp3s0f0": {Name: "enp3s0f0"},
 		"eth0": {
 			Address:          "01:01:01:01:01:01",
 			AddrAssignType:   &addrAssignType,

sysfs/pci_device.go

@@ -103,6 +103,19 @@ func (pd PciDevice) Name() string {
 	return pd.Location.String()
 }
 
+// PciDeviceVFAddress returns the PCI BDF address of a Virtual Function by
+// resolving the virtfn symlink at /sys/bus/pci/devices/<bdf>/virtfn<vfIndex>.
+func (fs FS) PciDeviceVFAddress(device *PciDevice, vfIndex uint32) (string, error) {
+	loc := device.Location
+	bdf := fmt.Sprintf("%04x:%02x:%02x.%x", loc.Segment, loc.Bus, loc.Device, loc.Function)
+	virtfnPath := fs.sys.Path(pciDevicesPath, bdf, fmt.Sprintf("virtfn%d", vfIndex))
+	resolved, err := os.Readlink(virtfnPath)
+	if err != nil {
+		return "", fmt.Errorf("failed to read virtfn%d symlink for %q: %w", vfIndex, bdf, err)
+	}
+	return filepath.Base(resolved), nil
+}
+
 // PciDevices is a collection of every PCI device in
 // /sys/bus/pci/devices .
 //

testdata/fixtures.ttar

@@ -6341,6 +6341,12 @@ Mode: 644
 Directory: fixtures/sys/class/net
 Mode: 755
 # ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Directory: fixtures/sys/class/net/enp3s0f0
+Mode: 755
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Path: fixtures/sys/class/net/enp3s0f0/device
+SymlinkTo: ../../../devices/pci0000:a2/0000:a2:00.0
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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